Device for sensing a broken yarn of a circular knitting machine

ABSTRACT

A device for sensing a broken yarn of a circular knitting machine of the type wherein are provided one or more latch needles which are elevationally movably positioned at the needle groove of a cylinder with one or more cam members to operate the latch needles with at least one sensing member disposed in the lower cam which is located under the latch needle butt with a means for generating an electrical signal when the latch needle falls by its own weight so that the butt touches the sensing member which is responsive thereto, and a mechanism for stopping the knitting machine, a means for feeding the electrical signal to the mechanism, and means for stopping the mechanism responsive to the transmission of the electrical signal to the mechanism.

United States Patent [191 Hino et al.

[451 Jan. 15, 1974 1 DEVICE FOR SENSING A BROKEN YARN OF A CIRCULAR KNITTING MACHINE [73] Assignee: Gunze Company, Ltd., Kyoto, Japan [22] Filed: July 23, 1971 211 Appl. No.: 165,492

[30] Foreign Application Priority Data July 29, 1970 Japan 45/6678 1 July 29, 1970 Japan 45/66782 [52] U.S. C1. 66/157, 66/163 [51] lnt. Cl. D04b 35/14 [58] Field 01 Search 66/157, 163, 165, 66/56; 192/1165, 144; 139/1 R, 1 E, 336

[56] References Cited UNITED STATES PATENTS 3,449,931 6/1969 Kawakami et a1. 66/157 2,779,448 l/1957 Lambach et a1. 66/157 X 3,509,739 5/1970 Gottschall 66/157 3,557,841 l/197l Moessinger.... 139/1 E 3,529,444 9/1970 Romoli 66/157 FOREIGN PATENTS OR APPLICATIONS 745,130 2/1956 Great Britain 66/157 182,368 5/1936 Switzerland 139/336 658,737 12/1963 Italy 66/56 257,804 10/1967 Austria 66/157 785,651 10/1957 Great Britain 66/157 Primary Examiner-James Kee Chi t nekxms as s nr 5 7 ABSTRACT A device for sensing a broken yarn of a circular knitting machine of the type wherein are provided one or 'more latch needles which are elevationally movably k the butt touches the sensing memlber which is responsive thereto, and a mechanism for stopping the knitting machine, a means for feeding the electrical signal to the mechanism, and means for stopping the mechanism responsive to the transmission of the electrical signal to the mechanism.

7 Claims, 22 Drawing Figures DEVICE FOR SENSING A BROKEN YARN OF A CIRCULAR KNITTING MACHINE This invention relates to a device for sensing a broken yarn, and more particularly to a device for sensing a broken yarn of a circular knitting machine.

It is generally well known a device for sensing broken yarn to automatically stop a knitting machine immediately when the yarn supplied to a latch needle is broken, a loop yarn is broken during loop knitting or the latch of a latch needle remains open so as not to knit a loop in a circular knitting machine. It is generally used as a device for sensing a broken yarn of the conventional circular knitting machine a device for stopping the knitting machine by disengaging a clutch in such a manner that the butt of a lower needle at a cylinder side urges a sensing member of lever shape when the latch needle, particularly lower needle at the cylinder side falls by its self-weight and inertia. Thus, it is common to utilize the lower neede at the cylinder side therefor.

However, when the knitting machine operates at high speed, this type of sensing device used in the knitting machine becomes too dull to sense to cause the knitting defects to be greatly expanded as its disadvantage. And, when the defective portion is again warped by the latch needle, it requires a greatdeal of trouble, and it is apprehended that the latch needle is damaged during its warping. Such occurrence of knitting defects introduces a great deal of loss such as production of yarn waste of knitted cloth. Further, it is necessary at the efficiency of the sensing member of lever shape that the member is disposed under the butt of the latch needle. For this reason, particularly when a loop is knitted, the butt of the latch needle becomes unstable owing to its high speed rotation with the result that the latch needle becomes feasible to vibrate. As a result, it is apprehended that it seriously affects the knitting of loop. In addition, since excessive load is applied to the butt, the butt or the stem of the latch needle are bent or the needle groove of the cylinder is also bent so as to obstruct accurate and smooth operation of the latch needle.

When the latch of the latch needle of the conventional device'for sensing a broken yarn isnot normally operated but is in a closed state, the contact of the device senses this so as to stop the knitting machine. In this case since the contact touches directly the latch of the latch needle, the latch is apt to be damaged. Furthermore, since the contact is provided on the side surface of the outside of the cylinder of the machine, it is complicated at all viewpoints of operation such as warping of cloth to the latch needle. And, since it is not preferable in operation to provide such contacts to all feeders, it is common to provide the contacts to every three or four feeders.

In accordance with the prior art, as exemplified by the Japanese Utility Model Publication No. 8650/55 published on June 23, 1955 entitled A device for opening and closing an electric circuit for automatic stop of circular knitting machine" applied by Nagata Seiki C0., Ltd., when the latch of the latch needle of the knitting machine is closed in abnormal state, a

contact touches the latch so that the shaft of thecontact rotates to stop the knitting machine. In the lap anese Patent Publication No. 920/69 published on Jan. 16, 1969 entitled A latch needle knitting machine applied by The Bentley Engineering C0., Ltd. of England, when the latch of the latch needle is closed in an abnormal state, the latch touches the latch switch so that the latch is opened and the switch is rotated simultaneously to stop the knitting machine. In the Japanese Pat. Publication No. 15223/ published on May 28, 1970 entitled A device for controlling stoppage of a knitting machine by the latch of a latch needle" corresponding to U.S. Pat. No. 3,509,739 issued on May 5, 1970 entitled Stop motion for a knitting machine ap plied by Franz Morat Gmbl-L of Germany, when the latch of the latch needle of the knitting machine is closed in abnormal state, a resilient feeler contact senses this as as to stop the knitting machine. Further, in U.S. Pat. No. 2,963,890 issued on Dec. 13, 1960 entitled Electrical stop motion for knitting machines applied by James M. Hoots, when the electrical conductor wire 31 of the detector 30 of the knitting machine touches the latch of the latch needle, the needle is drawn so as to stop the knitting machine through an electric circuit.

In the circular knitting machine known per se, it has two types of needles, lower needles provided at the cylinder side and upper needles provided at the dial side, and the conventional device for sensing a broken yarn is installed at the lower needle of the cylinder side.

This invention contemplates to eliminate the aforementioned disadvantages of the conventional knitting machine by providing a device for sensing a broken yarn not only to the lower needle at the cylinder side but to the upper needle at the dial side so as to utilize it at the upper needle of the dial side to overcome the problem owing to the utilization of the lower needle at the same time to prevent the occurrence of knitting defects due to the upper needle. Thus, this'invention has devised to accurately sense rapidly a broken yarn at not only lower needle but upper needle so as to abruptly stop the knitting machine thereby particularly in high speed knitting machine.

According to one aspectof the present invention, a knitting machine comprises a sensing member provided in the cam disposed at the rear of a latch needle butt of cams for operating the latch needles and a mechanism for stopping the knitting machine. by utilizing the touching action of the butt when the latch needle moves by its inertia due to broken yarn so that the butt touches the sensing member.

It is, therefore, a primary object of this invention is to provide a device for stopping a mechanism for stopping a knitting machine which comprises a sensing member provided in the lower cam disposed under the latch needle butt of cams for operating the latch needle at the cylinder side of the machine wherein when the lower needle fallsby its self-weight and inertia due to broken yarn, the lower needle butt touches the sensing member so as to utilize the touching action as a signal for operating the mechanism.

It is another object of this invention to provide a device for stopping a mechanism for stopping a knitting machine which comprises a sensing member provided in the cam disposed at the rear of an upper needle butt of cams for moving the upper needles back and forth at the dial side of the machine wherein when the upper needle moves by its inertia due to a broken yarn, the butt touches the sensing member so as to utilize the touching action as a signal for operating the mechanism.

It is a further object of this invention to provide a knitting machine which is not apprehended to produce a great deal of waste of knitted cloth by restraining knitting defects to a minimum so as to stop the rotation of the machine due to its inertia to abruptly stop it.

It is still another object of the invention to provide a knitting machine which comprises a sensing member provided in a cam so as to accurately detect abruptly a broken yarn, knitting defects and impossibility of loop knitting but not to be apprehended to damage the stern of the needle and the butt or to bend the needle groove as heretofore particularly not to be necessary to check the upper needle every time when knitting defect occurs by the upper needle.

It is still another object of the invention to provide a knittingmachine which comprises a sensing member provided in a cam at each feeder without any inconvenience in operation of the machine different from the conventional one which has a sensing member provided at the outside of the cylinder.

It is a more specific object of this invention to provide a knitting machine which comprises a sensing member provided in a cam so that the cam may better control the travel of the needle different from the conventional one which has a sensing member of lever type under the butt of the latch needle, particularly that the latch needle may not vibrate even in high speed operation of the machine in order to provide excellent knitting operation.

The other features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a front view of the latch needle or lower needle at the cylinder side with a device for sensing broken yarn of this invention in a circular knitting machine;

FIG. 2 is a side sectional view of FIG. 1;

FIG. 3 is a side sectional view of the latch needle or upper needle at the dial side with a device for sensing broken yarn of this invention in a circular knitting machine;

FIG. 4 is a plan view of FIG. 3;

FIG. 5 is an explanatory view of one example of an electric circuit of the device for sensing broken yarn of this invention;

FIG. 6 is a wiring diagram of the detail of the electric circuit shown in FIG. 5;

FIG. 7 is an explanatory view of one example of a mechanism for stopping the knitting machine by the operation of the device for sensing broken yarn of this invention;

FIGS. 8a-8f are detailed views of one example of the sensing member of this invention;

FIGS. 9a-9e are detailed views of another example of the sensing member of this invention similar to FIGS.

FIGS. 10a-l0d are detailed views of a further example of the sensing member of this invention similar to FIGS. 8a-8f.

Reference is now made to the drawings, particularly to FIGS. 1 and 2, which show the latch needle or lower needle at the cylinder side with a device for sensing broken yarn of this invention in a circular knitting machine, and the device for sensing a broken yarn may be applied to the lower and upper needles of a circular knitting machine, and the application to the lower needle will now be described.

A latch needle 1 having a butt 2 is elevationally and movably disposed in each needle groove 3' of a cylinder 3. There is provided an upper cam 5 and lower cams 6a and 6b for operating the latch needle 1. In this invention, a sensing member 7 for sensing a broken yarn is provided in the lower cam 6a disposed under the the butt 2. During knitting, the needle 1 advances in the direction of the arrow of FIG. I, with the upper face 2a of the butt 2 kept in contact with the cam face of the upper cam 5 all the time. More specifically, the sensing member 7 is disposed in the lower cam below a slanting cam face 5' of the upper cam 5, forwardly of the same cam face 5 with respect to the direction of advance of the needle I, so that if a yarn supplied to the needle 1 is broken or a loop yarn is broken, permitting the needle 1 to fall under gravity and by inertia, the lower face 2b of the butt 2 comes into contact with the sensing member 7.

The sensing member 7 converts the touching action of the butt 2 thereto into an electric signal which is fed to a mechanism for stopping the knitting machine so as to abruptly stop theknitting machine.

The sensing member 7 may be made of a metal plate the material of which may be any of electroconductive metal material such as iron, electroconductive alloy steel (nickel-chromium alloy, stainless steel, etc.), copper, copper alloy, aluminium, aluminium alloy and so on. The configuration of the sensing member 7 may not always be a thin plate, but may be a block or lump, and its shape is not limited. However, the part contacting the machine side of the sensing member is made electrically of insulating material such as synthetic resin, but the part contacting the needle butt 2 is not insulated.

Referring now to FIGS. 8 to 10, which show examples of the sensing member of this invention, and particularly to FIG. 8, the sensing member 7 is fixed at one end thereof to a synthetic resin insulator 6c secured to the lower cam 6a and is free at the other end. In FIG. 9, the sensing member 7 is fixed to the lower cam 6a through an insulator 6c, and in FIG. 10, the sensing member 7 is intalled at the position shown in the drawing of the lower cam 6a.

One embodiment of the device for sensing a broken yarn for the latch needle or lower needle at the cylinder side has heretofore been described, and another embodiment of the device for sensing a broken yarn for the latch needle or upper needle at the dial side will now be described with reference to FIGS. 3 and 4, which show the latch needle or upper needle at the dial side with a device for sensing broken yarn of this invention in a circular knitting machine.

An upper needle 1 has a butt 2 and is so inserted into a needle groove 4 of a dial 3a as to move back and forth in the radial direction. There is provided cams 5 and 6 for operating the upper needle 1. A sensing member 7 made of metal plate is disposed within the cam 6 disposed at the rear of the butt 2 of the upper needle 1.

During knitting operation, the needle 1 advances in the direction of the arrow in FIG. 4, with the upper face (i.e., outer face) 2a of the butt 2 in contact with the cam face of the outer cam 5 all the time. When the yarn is broken, the upper needle 1 advancing in contact with the cam face is guided along a slanting cam face 5, with the result that the lower face (i.e., inner face) 2b of its butt 2 touches the sensing member 7 which is mounted in the inner cam 6 positioned approximately on a line extending from the slanting cam face 5', whereupon the sensing member 7 converts the touching action of the butt 2 thereto into an electrical signal, which is fed to the mechanism for stopping the knitting machine so as to abruptly stop the machine similarly to the operation described with reference to FIGS. 1 and 2.

Reference is now made to FIGS.,5 and 6, which show the electric circuits of the device for generating an electrical signal upon touching of the sensing member 7 to the latch needle butt 2.

In FIG. 5, a plurality of thyristors 8 are shown, and it is so constructed that if the latch needle butt 2 touches the sensing member 7, minute electric current flows through the gate electrode 9 of the thyristor 8.

' The sensing member 7 is thus connected to the gate electrode 9 of the thyristor 8 by a shield wire, and a voltage of several volts such as 3 volts is applied to the machine body or latch needle touching the machine. Therefore, if the latch needle butt 2 touches the sensing member7 due to the breakage of the knitted yarn, the voltage such as, for example, 3 volts is applied to the gate electrode 9. If this voltage is applied to the thyristor 8, the thyristor 8 loses its current shutting-off characteristic so that an electric current starts to continuously flow from its positive to negative electrodes to light a'warning lamp 10. And, a relay R0 is energized so as to open the contact of the relay to cause an electromagnetic clutch 29a tobe shut off at the same time to cause an electromagnetic brake 29b to be energized thereby so as to stop the rotation of the knitting machine. Here, the relay R0 and thyristor 8 are reset to theoriginal state by depressing a push-button switch PB. 1

Thus, the damage of the latch needle 1 and the portion of the breakage of the yarn are indicated thereby.

The sensing member 7 and the thyristor 8 are provided at each feeder of the knitting machine. In FIG. 5, reference numeral 11 illustrates an OR circuit such as made of diode, etc., which energizes a mechanism 12 for stopping the knitting machine if any of the thyristors 8 is operated, to abruptly stop the machine. Numeral 13 shows an indicator lamp which indicates the stoppage of the machine upon breakage of the yarn.

Reference is now made to FIG. 7, which shows one example of a mechanism for stopping the knitting machine by the operation of the device for sensing broken yarn of this invention.

In the mechanism 12 for stopping the knitting machine, a pulley 14 is rotatably engaged with a shaft 15 and is driven by a prime mover with a transmission (not shown). An electromagnetic plate 16 containing an electromagnet is provided integrally with the pulley 14 and is engaged rotatably with respect to the shaft 15. A rotary plate 18 fixed to the shaft 15 and a friction plate 17 rotatably engaged with the shaft 15 are connected through pins 19 so that the friction plate 17 is slidably along the shaft 15. When the electromagnetic plate 16 is magnetized upon an energizing coil 29a being energized, the friction plate 17 is closely contacted with the electromagnetic plate 16.

A belt 23 is engaged between a pulley 20 fixed to the shaft 15 and a pulley 21 fixed to another shaft 22. An electromagnetic plate 24 rotatably engaged with the shaft 15 includes an electromagnet having an energizing coil 29b and is fixed to a fixing member 25 so that it is impossible to be rotatable. A :rotary plate 27 fixed to the shaft 15 and a friction plate 26 rotatably engaged with the shaft 15 are connected through pins 28 so that the friction plate 26 may be slidable axially. Therefore, if the energizing coil 29b is energized to magnetize the electromagnetic plate 24, is closely contacted with the plate 24. Here, the pulley 20 and the rotary plates 18 and 27 are provided integrally.

A gear 30 is fixed to the transmission shaft 22, and

the cylinder 3 and dial 3a of the knitting machine are rotated through a gear 31 engaged with the gear 30. If the OR circuit 11 is operated, one electromagnetic plate 16 on the shaft 15 is stopped at the same time the other electromagnetic plate 24 is operated simultaneously.

It should be understood that the above description with reference to FIGS. 5 and 6 is entirely the same to a device for sensing broken yarn for not only the latch needle at the cylinder side but the latch needle at the dial side and a mechanism for stopping the knitting machine interlocked with the sensing; device.

The foregoing description, and. the accompanying drawings show illustrative forms of construction according to this invention, but it will be understood that these forms are not restrictive, and that the invention may be practiced in many ways within the scope of the appended claims.

What we claim is: i

1. A device for sensing a broken yarn in a circular knitting machine of the type in which at least one latch needle is elevationallymovably provided at the needle groove of a cylinder thereof comprising in combination at least one cam means for operating the latch needle to guide the same during a knitting operation with a butt of the needle in contact with a cam face of an upper cam all the time, at least one sensing member mounted only in a lower cam disposed under the latch needle butt and positioned approximately on a line extending from a slanting cam face of the upper cam, means for generating an electrical signal when the latch needle falls out of engagement with a yarn under gravity and by its inertia so that the butt directly-touches said sensing member responsive thereto, a mechanism for stopping the knitting machine, means for feeding the electric signal to said mechanism, and means for stopping the mechanism responsive to the transmission of the electrical signal to the mechanism.

2. A device for sensing a broken yarn in a circular knitting machine of the type in which at least one latch needle is radially movably provided at the needle groove of a dial thereof comprising in combination at least one cam means for operating; the latch needle to guide the same during a knitting operation with a butt of the needle in contact with a cam face of an outer cam all the time, at least one sensing member mounted only in an inner cam disposed inwardly of the needle butt and positioned approximately on a line extending from a slanting cam face of said outer cam, means for generating an electric signal when the needle moves out of the engagement with a yarn so that the butt directly touches said sensing member responsive thereto, a mechanism for stopping the knitting machine, means for feeding the electrical signal to said mechanism, and means for stopping the mechanism responsive to the transmission of the electrical signal to the mechanism.

3. The device according to claim 1, wherein said mechanism comprises a prime mover, a first pulley for said prime mover, a shaft a second pulley rotatably engaged with said shaft, a belt engaged with said first and second pulleys, a first electromagnetic plate containing an electromagnet provided integrally with said second pulley engaged movably with said shaft engaged movably with said shaft, a first rotary plate fixed to said shaft, a first friction plate movably engaged with said shaft and connected to said first rotary plate through pins and closely contacting said first electromagnet plate responsive to the magnetization of said first electromagnetic plate, a third pulley fixed to said shaft, another transmission shaft, a fourth pulley fixed to said transmission shaft, a belt engaged between said third and fourth pulleys, a second electromagnetic plate containing an electromagnet engaged movably with said shaft and fixed to a fixing member, a second rotary plate fixed to said shaft, a second friction plate movably engaged with said shaft and connected to said second rotary plate through another pins and closely contacting with said second electromagnetic plate upon magnetization of said second electromagnetic plate, a gear fixed to said transmission shaft, a second gear engaged with said gear, wherein simultaneously when said first electromagnetic plate is magnetized, said second electromagnetic plate is demagnetized, said first friction plate is closely contacted with said first electromagnetic plate, said second friction plate and said second electromagnetic plate are separated so that said shafts are driven so as to rotate the knitting machine, and when the latch needle touches said sensing member to operate said relay, said first electromagnetic plate is demagnetized at the same time said second electromagnetic plate is magnetized, said first friction plate and said first electromagnetic plate are separated, said second friction plate is closely contacted with said second electromagnetic plate so that said shafts are stopped to rotate so as to stop the rotation of the knitting machine.

4. The device according to claim 2, wherein said mechanism comprises a prime mover, a first pulley for said prime mover, a shaft, a second pulley rotatably engaged with said shaft, a belt engaged with said first and second pulleys, a first electromagnetic plate containing an electromagnet provided integrally with said second pulley engaged movably with said shaft engaged movably with said shaft, a first rotary plate fixed to siad shaft, a first friction plate movably enaged with said shaft and connected to said first rotary plate through pins and closely contacting said first electromagnetic plate responsive to the magnetization of said first electromagnetic plate, a third pulley fixed to said shaft, another transmission shaft, a fourth pulley fixed to said transmission shaft, a belt engaged between said third and fourth pulleys, a second electromagnetic plate containing an electromagnet engaged movably with said shaft and fixed to a fixing member, a second rotary plate fixed to said shaft, a second friction plate movably engaged with said shaft and connected to said second rotary plate through another pins and closely contacting with said second electromagnetic plate upon magnetization of said second electromagnetic plate, a gear fixed to said transmission shaft, a second gear engaged with said gear, wherein simultaneously when said first electromagnetic plate is magnetized, said second electromagnetic plate is demagnetized, said first friction plate is closely contacted with said first electromagnetic plate, said second friction plate and said second electromagnetic plate are separated so that said shafts are driven so as to rotate the knitting machine, and when the latch needle touches said sensing member to operate said relay, said first electromagnetic plate is demagnetized at the same time said second electromagnetic plate is magnetized, said first friction plate and said first electromagnetic plate are separated, said second friction plate is closely contacted with said second electromagnetic plate so that said shafts are stopped to rotate so as to stop the rotation of the knitting machine.

5. The device according to claim 1, wherein said means for generating an electrical signal includes an OR circuit including at least one thyristor and a diode, and an indicator lamp.

6. The device according to claim 2, wherein said means for generating an electrical signal includes an OR circuit including at least one thyristor and a diode, and an indicator lamp.

7. A device for sensing a broken yarn of a circular knitting machine of the type in which at least one lower latch needle is elevationally movably provided at the needle groove of a cylinder thereof and at least one upper latch needle is radially movably provided at the needle groove of a dial thereof comprising in combination cam means for operating the latch needles to guide the same during a knitting operation with butts of the needles in contact with cam faces of an upper cam and an outer cam all the time, sensing members mounted only in a lower cam and in and inner cam disposed under and inwardly of the needle butts respectively and positioned approximately on lines extending from slanting cam faces of said upper and outer cams, means for generating an electric signal when the needles move out of engagement with the yarn back toward said lower cam and inner cam so that the butts directly touch said sensing members responsive thereto, a mechanism for stopping the knitting machine, means for feeding the electrical signal to said mechanism, and means for stopping the mechanism responsive to the transmission of the electrical signal to the mechanism. =l 

1. A device for sensing a broken yarn in a circular knitting machine of the type in which at least one latch needle is elevationally movably provided at the needle groove of a cylinder thereof comprising in combination at least one cam means for operating the latch needle to guide the same during a knitting operation with a butt of the needle in contact with a cam face of an upper cam all the time, at least one sensing member mounted only in a lower cam disposed under the latch needle butt and positioned approximately on a line extending from a slanting cam face of the upper cam, means for generating an electrical signal when the latch needle falls out of engagement with a yarn under gravity and by its inertia so that the butt directly touches said sensing member responsive thereto, a mechanism for stopping the knitting machine, means for feeding the electric signal to said mechanism, and means for stopping the mechanism responsive to the transmission of the electrical signal to the mechanism.
 2. A device for sensing a broken yarn in a circular knitting machine of the type in which at least one latch needle is radially movably provided at the needle groove of a dial thereof comprising in combination at least one cam means for operating the latch needle to guide the same during a knitting operation with a butt of the needle in contact with a cam face of an outer cam all the time, at least one sensing member mounted only in an inner cam disposed inwardly of the needle butt and positioned approximately on a line extending from a slanting cam face of said outer cam, means for generating an electric signal when the needle moves out of the engagement with a yarn so that the butt directly touches said sensing member responsive thereto, a mechanism for stopping the knitting machine, means for feeding the electrical signal to said mechanism, and means for stopping the mechanism responsive to the transmission of the electrical signal to the mechanism.
 3. The device according to claim 1, wherein said mechanism comprises a prime mover, a first pulley for said prime mover, a shaft, a second pulley rotatably engaged with said shaft, a belt engaged with said first and second pulleys, a first electromagnetic plate containing an electromagnet provided integrally with said second pulley engaged movably with said shaft engaged movably with said shaft, a first rotary plate fixed to said shaft, a first friction plate movably engaged with said shaft and connected to said first rotary plate through pins and closely contacting said first electromagnetic plate responsive to the magnetization of said first electromagnetic plate, a third pulley fixed to said shaft, another transmission shaft, a fourth pulley fixed to said transmission shaft, a belt engaged between said third and fourth pulleys, a second electromagnetic plate containing an electromagnet engaged movably with said shaft and fixed to a fixing member, a second rotary plate fixed to said shaft, a second friction plate movably engaged with said shaft and connected to said second rotary plate through another pins and closely contacting with said second electromagnetic plate upon magnetization of said second electromagnetic plate, a gear fixed to said transmission shaft, a second gear engaged with said gear, wherein simultaneously when said first electromagnetic plate is magnetized, said second electromagnetic plate is demagnetized, said first friction plate is closely contacted with said first electromagnetic plate, said second friction plate and said second electromagnetic plate are separated so that said shafts are driven so as to rotate the knitting machine, and when the latch needle touches said sensing member to operate said relay, said first electromagnetic plate is demagnetized at the same time said second electromagnetic plate is magnetized, said first friction plate and said first electromagnetic plate are separated, said second friction plate is closely contacted with said second electromagnetic plate so that said shafts are stopped to rotate so as to stop the rotation of the knitting machine.
 4. The device according to claim 2, wherein said mechanism comprises a prime mover, a first pulley for said prime mover, a shaft, a second pulley rotatably engaged with said shaft, a belt engaged with said first and second pulleys, a first electromagnetic plate containing an electromagnet provided integrally with said second pulley engaged movably with said shaft engaged movably with said shaft, a first rotary plate fixed to said shaft, a first friction plate movably enaged with said shaft and connected to said first rotary plate through pins and closely contacting said first electromagnetic plate responsive to the magnetization of said first electromagnetic plate, a third pulley fixed to said shaft, another transmission shaft, a fourth pulley fixed to said transmission shaft, a belt engaged between said third and fourth pulleys, a second electromagnetic plate containing an electromagnet engaged movably with said shaft and fixed to a fixing member, a second rotary plate fixed to said shaft, a second friction plate movably engaged with said shaft and connected to said second rotary plate through another pins and closely contacting with said second electromagnetic plate upon magnetization of said second electromagnetic plate, a gear fixed to said transmission shaft, a second gear engaged with said gear, wherein simultaneously when said first electromagnetic plate is magnetized, said second electromagnetic plate is demagnetized, said first friction plate is closely contacted with said first electromagnetic plate, said second friction plate and said second electromagnetic plate are separated so that said shafts are driven so as to rotate the knitting machine, and when the latch needle touches said sensing member to operate said relay, said first electromagnetic plate is demagnetized at the same time said second electromagnetic plate is magnetized, said first friction plate and said first electromagnetic plate are separated, said second friction plate is closely contacted with said second electromagnetic plate so that said shafts are stopped to rotate so as to stop the rotation of the knitting machine.
 5. The device according to claim 1, wherein said means for generating an electrical signal includes an OR circuit including at least one thyristor and a diode, and an indicator lamp.
 6. The device according to claim 2, wherein said means for generating an electrical signal includes an OR circuit including at least one thyristor and a diode, and an indicator lamp.
 7. A device for sensing a broken yarn of a circular knitting machine of the type in which at least one lower latch needle is elevationally movably provided at the needle groove of a cylinder thereof and at least one upper latch needle is radially movably provided at the needle groove of a dial thereof comprising in combination cam means for operating the latch needles to guide the same during a knitting operation with butts of the needles in contact with cam faces of an upper cam and an outer cam all the time, sensing members mounted only in a lower cam and in and inner cam disposed under and inwardly of the needle butts respectively and positioned approximately on lines extending from slanting cam faces of said upper and outer cams, means for generating an electric signal when the needles move out of engagement with the yarn back toward said lower cam and inner cam so that the butts directly touch said sensing members responsive thereto, a mechanism for stopping the knitting machine, means for feeding the electrical signal to said mechanism, and means for stopping the mechanism responsive to the transmission of the electrical signal to the mechanism. 